Hydronephrosis is a condition where one or both kidneys become stretched and swollen as the result of a build-up of urine inside them.

It can affect people of any age and is sometimes spotted in unborn babies during routine pregnancy ultrasound scans (this is known as antenatal hydronephrosis).

Hydronephrosis doesn’t generally cause any long-term problems if it’s diagnosed and treated promptly. Babies with the condition may not require any treatment at all.

However, the condition can increase your chances of getting urinary tract infections (UTIs). In severe cases that are left untreated, the kidney(s) may become scarred, which could lead to loss of kidney function (kidney failure).

Hydronephrosis in babies

Hydronephrosis is increasingly being found in unborn babies during routine ultrasound scans. This is known as antenatal hydronephrosis. It’s estimated to occur in at least 1 in every 100 pregnancies.

As a parent, it can be worrying to learn your baby has a problem with their kidneys. However, most cases of hydronephrosis in babies aren’t serious and shouldn’t affect the outcome of your pregnancy.

About four out of every five cases will resolve on their own before or within a few months of birth and will cause no long-term problems for you or your baby. The remaining cases may require treatment with antibiotics to prevent kidney infections, and in some cases surgery may be needed.

Read more about diagnosing antenatal hydronephrosis and treating antenatal hydronephrosis.

Signs and symptoms

Hydronephrosis doesn’t always cause symptoms. If it does, these may develop quickly over a few hours or gradually over weeks or months.

Symptoms can include:

  • pain in your back or side – this may be sudden and severe, or may be a dull ache that comes and goes over time; it may get worse after you’ve drunk a lot
  • symptoms of a UTI, such as a high temperature (fever) of 38C (100.4F) or above, chills and feeling or being sick
  • blood in your urine
  • urinating less often than you used to or with a weak stream
  • in severe cases, noticeably swollen kidneys

You should see your GP if you develop severe or persistent pain in your back or side, have symptoms of a UTI, or notice a change in how often you urinate. They may refer you for an ultrasound scan to assess your kidneys.

Hydronephrosis in babies doesn’t usually cause symptoms, but you should seek medical advice as soon as possible if your child develops signs of a possible UTI, such as a high fever without any other obvious cause.

Read more about diagnosing hydronephrosis.

What causes hydronephrosis?

Hydronephrosis diagnosed in pregnancy is usually mild. It is thought to be caused by an increase in the amount of urine your baby produces in the later stages of pregnancy.

In more severe cases, it may be caused by a blockage in the flow of urine from the kidney(s) to the bladder, backflow of urine from the bladder to the kidney(s), or a blockage in the flow of urine out of the bladder.

In adults, hydronephrosis is commonly caused by:

Read more about the causes of hydronephrosis.

Treating hydronephrosis

If you have hydronephrosis, your treatment will depend on what’s causing the condition and how severe it is. Pregnant women and babies with the condition may not require any treatment.

In adults, the first stage of treatment is often to drain the urine out of your kidneys by inserting a tube called a catheter into your bladder or kidney(s). This will help relieve the pressure on your kidneys.

Once the pressure has been relieved, the cause of the build-up of urine may need to be treated. The treatments used will depend on why the condition developed. For example:

  • kidney stones may be removed during an operation or broken up using sound waves
  • an enlarged prostate can be treated with medication or surgery to remove some of the prostate
  • blockages in the ureters can be treated using surgery to insert a small tube called a stent
  • cancer may be treated using a combination of chemotherapy, radiotherapy or surgery to remove the cancerous tissue

Read more about how hydronephrosis is treated.

Causes of hydronephrosis

Hydronephrosis is usually caused by a blockage in the urinary tract or something disrupting the normal workings of the urinary tract.

The urinary tract is made up of the kidneys, the bladder, the ureters (the tubes that run from the kidney to the bladder) and the urethra (the tube that carries urine out of the body).

A blockage or problem in the urinary tract can mean urine is unable to drain from the kidneys or is able to flow the wrong way up into the kidneys. This can lead to a build-up of urine in the kidneys, causing them to become stretched and swollen.

Causes of hydronephrosis in adults

Some of the main causes of hydronephrosis in adults include:

  • kidney stones – small stones that form in the kidneys that can sometimes travel out of a kidney and block the ureters
  • benign prostatic hyperplasia – non-cancerous swelling of the prostate gland in men
  • pregnancy – during pregnancy the enlarged womb (uterus) can sometimes place pressure on the ureters
  • narrowing of the ureters – this can occur as a result of injury to the ureter, infection or surgery
  • pelvic organ prolapse – where one or more of the pelvic organs bulge into the vagina
  • neurogenic bladder – damage to the nerves that control the bladder
  • cancers in or around the urinary tract – such as bladder cancerkidney cancerprostate cancercervical cancerovarian cancer or womb cancer

Less commonly, the urinary tract can become blocked or squashed by a blood clotendometriosis (where tissue that behaves like the lining of the womb is found outside the womb) or ovarian cysts (fluid-filled sacs in the ovaries).

Causes of hydronephrosis in babies

Sometimes it’s not clear why hydronephrosis develops in unborn babies (antenatal hydronephrosis). It’s thought it often may be caused by an increase in the amount of urine your baby produces in the later stages of pregnancy.

Usually the kidneys themselves are normal and the condition gets better by itself before or within a few months of birth.

In some cases, it can be caused by:

  • a blockage or narrowing in the urinary tract – this is sometimes caused by the growth of excess tissue, but often there’s no clear cause
  • vesicoureteral reflux – where the valve that controls the flow of urine between the bladder and the ureters doesn’t function properly, allowing urine to flow back up to the kidneys

These problems will often get better on their own, although occasionally your baby may need to have surgery to correct them.

It’s extremely rare for hydronephrosis in babies and children to be caused by a tumour or kidney stones.

Diagnosing hydronephrosis

Hydronephrosis is usually diagnosed using an ultrasound scan. Further tests may be needed to find out the cause of the condition.

An ultrasound scan uses sound waves to create a picture of the inside of your kidneys. If your kidneys are swollen, this should show up clearly.

Further tests

You may need a number of additional tests to help determine the cause of hydronephrosis. These may include:

  • blood tests – used to check for infection
  • urine tests – used to check for infection as well as traces of blood (this could be caused by a kidney stone)
  • intravenous urography – an X-ray of your kidneys that’s taken after a special dye has been injected into your bloodstream; the dye highlights the flow of urine through your urinary tract, which can be useful for identifying any blockages
  • a computerised tomography (CT) scan – similar to an X-ray, but uses multiple images and a computer to build up a three-dimensional picture of the inside of your body

Diagnosing hydronephrosis in babies

Hydronephrosis may be diagnosed in your baby while you’re pregnant, usually during a routine pregnancy ultrasound scan at around 20 weeks. This is known as antenatal hydronephrosis.

If your baby is diagnosed with antenatal hydronephrosis, you may need to have extra ultrasound scans during your pregnancy to check your baby is growing normally and their kidneys are not getting too large.

In most cases, the problem will improve before your baby is born or within a few months afterwards. Your baby may need to have scans after they’re born to monitor their condition and see if treatment is necessary.

Read more about treating antenatal hydronephrosis.

Treating hydronephrosis

Treatment for hydronephrosis depends on what’s causing the condition and how severe it is.

In adults, the aims of treatment are to:

  • remove the build-up of urine and relieve the pressure on your kidney(s)
  • prevent permanent kidney damage
  • treat the underlying cause

Most people with hydronephrosis will have a procedure called catheterisation to drain the urine from their kidney(s). Depending on the underlying cause, medication or surgery may be needed afterwards to correct the problem.

If the condition is severe or causing problems such as a urinary tract infection (UTI), you may to be treated soon after you’re diagnosed. In less severe cases, it may be safe to delay treatment for a short period.

Draining the urine

The first stage in treating hydronephrosis is to drain the urine out of your kidneys. This will help ease your pain and prevent any further damage to your kidneys.

A thin tube called a catheter may be inserted into your bladder through your urethra (the tube that carries urine out of the body) or directly into your kidney through a small cut in your skin.

Read more about urinary catheterisation.

In a few cases where one of the kidneys has already been severely damaged, it may be better to remove the affected kidney. Most people can function normally with just one working kidney, which won’t usually have a significant effect on your health or lifestyle.

Treating the underlying cause

Once the pressure on your kidney(s) has been relieved, the cause of the build-up of urine may need to be treated.

Some possible causes and their treatments are described below:

  • kidney stones can be removed during an operation or broken up using sound waves – read more about treating kidney stones
  • an enlarged prostate can be treated with medication or surgery to remove some of the prostate – read more about treating prostate enlargement
  • narrowing of the ureter (the tube that runs from the kidney to the bladder) can be treated by inserting a hollow plastic tube called a stent, which allows urine to flow through the narrowed section – this can often be done without making cuts in your skin
  • cancer that’s causing hydronephrosis may be treated using chemotherapyradiotherapy or surgery to remove the cancerous tissue

If hydronephrosis occurs because you’re pregnant, you won’t usually need any treatment because the condition will pass within a few weeks of giving birth.

In the meantime, catheters can be regularly used to drain urine from the kidney(s). Painkillers and antibiotics can also be given if you’re in pain or develop a UTI.

Treating hydronephrosis in babies

Most babies diagnosed with hydronephrosis before they’re born (antenatal hydronephrosis) won’t need any treatment because the condition will improve before they’re born or within a few months of their birth.

There’s usually no risk to you or your child, so labour shouldn’t need to be started early. After the birth, your baby may be examined to check for any obvious problems, such as swollen kidneys, but normally you’ll be able to take them home with you.

Your baby may need to return to hospital for some scans during the next few weeks to check there aren’t any continuing problems. These scans may include:

  • an ultrasound scan – where sound waves are used to create a picture of your baby’s kidneys
  • a micturating cystourethrogram (MCUG) – where a thin tube is used to pass a special type of liquid that shows up clearly on X-rays into your baby’s bladder while a series of X-rays are taken
  • a dimercaptosuccinic acid (DMSA) scan or MAG-3 scan – where your baby is injected with a substance that shows up on a special device called a gamma camera; the camera is then used to take pictures of your child’s kidneys

In most children, hydronephrosis will get better as they get older. But until scans show there’s no longer a problem, your child may need to take antibiotics to reduce their chances of developing a UTI as the urine inside their kidneys can make them more vulnerable to infection.

If hydronephrosis doesn’t get better by itself, your child may need to keep taking antibiotics. Occasionally, surgery may be recommended to treat the underlying cause of the condition.